Aesthetic effects of natural tooth color and semi-transparent gradual change are produced by superposing dental enamel and dentine with an interface of enamel-dentine junction. To solve the problem that beauty and strength cannot be guaranteed at the same time for pure-zirconia ceramic crown of molar tooth, one effective approach is to develop a type of zirconia ceramic which has a gradient gradual change in optical color and can be processed with Computer Aided Design (CAD)/Computer Aided Manufacturing (CAM), by simulating structure and optical characteristics of the tooth. Basis for such structure simulation is to learn a complete modality of the curved surface of the enamel-dentine junction. In the research of the enamel-dentine junction modality, Document 1 (Anthony J. Olejniczak, Lawrence B, et al. Quantification of dentine shape in anthropoid primates[J]. Ann Anat, 2004, 186: 479-485) and Document 2 (Smith T. M, Olejniczak A. J, Reid D. J, et al. Modern human molar enamel thickness and enamel-dentine junction shape[J]. Archives of Oral Biology, 2006, 51: 974-995) study a modality of the enamel-dentine junction in some axial plane of the tooth, and the obtained enamel-dentine junction is a line other than a plane. Document 3 (Rodrigo Borges Fonseca, Francisco Haiter-Neto, Alfredo J. Fernandes-Neto, et al. Radiodensity of enamel and dentin of human, bovine and swine teeth[J]. Archives of Oral Biology, 2004, 49:919-922) acquires a complete curved surface of the enamel-dentine junction through Micro-CT (Computed Tomography). Document 4 (Robert S, Corruceini. The Dentinoenamel Junction in Primates[J]. International Journal of Primatology, 1987, 8(2): 99-114), Document 5 (Bertram S, Kraus. Morphologic relationships between enamel and dentin surfaces of lower first molar teeth[J]. J. D. Res, 1952, 31(2):248-256) and Document 6 (Panaghlotis Bazos, Pascal Magne. Bio-emulation: biomimetically emulating nature utilizing a histo-anatomic approach; structural analysis[J]. The European journal of esthetic dentistry, 2011, 6(1): 8-19) acquire a complete curved surface of the enamel-dentine junction using a method of selectively removing enamel with acid demineralization. The two methods using Micro-CT and acid demineralization can be applied only on isolated teeth but not live natural teeth, because ray dose in Micro-CT is large, and the acid demineralization method is destructive. As a result, it is difficult to collect a number of samples required to establish an enamel-dentine junction database. Document 7 (Xiaojing Wang. Research on feasibility of creating 3D mortality of enamel-dentine junction surface with cone-beam CT[D]. Peking University Health Science Center, Beijing, 2012) can acquire the mortality of enamel-dentine junction surface without tooth damage by using cone-beam CT scanning in combination with image segmentation technology.
Document 8 (Kurbad A. Three-dimensionally layered ceramic blocks[J]. Int J Comput Dent, 2010, 13(4): 351-65) attempts to build a 3D laminated structure resembling a natural dental crown in a full-ceramic block. The ceramic block is structured so that the inner ceramic part emulates the optical characteristics of dentine, the outer ceramic part emulates the optical characteristics of enamel, and an interface between the two parts is cone-shaped. This can emulate, to some extent, semi-transparency and gradual change in color of natural crown, while it is inaccurate to assume the enamel-dentine junction as cone-shaped.
A statistical shape model is a model created from corresponding sets of mark points in surfaces of anatomic structures of interest in a single individual at different moments or between different individuals at the same moment. Creation of the statistical shape model is on the premise of acquisition of corresponding mark point sets between anatomic structures. Document 9 (Shen L, Makedon F S. Spherical mapping for processing of 3-D closed surfaces. Image and Vision Computing, 24(7): 743-761, 2006) proposes a Spherical Harmonic Description (SPHARM) which determines correspondence between structures through normalization of parametric space. Statistical modeling and analysis with SPHARM require that input grids should be genus-zero surfaces, i.e., the module should have a spherical topology. The enamel-dentine junction, however, is an interface between two different mineralized tissues of epithelium and extracellular matrix, and has an unclosed surface in a shell shape.